Large-scale preparation method of iron-based superconducting tape with barrier layer as outer sheath

Abstract

The invention discloses a large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer sheath. Firstly, a three-layer composite wrapped iron-based superconducting wire with copper as the outermost layer, a barrier layer material as the secondary outer layer and silver as the inner layer is prepared, a barrier layer is made of common materials with large hardness such as niobium and titanium, then a copper wrapping sleeve is completely corroded, the barrier layer is used as an outer wrapping sleeve to roll a strip through a flat roller, and an annealing process is added in the rolling process. And finally, the finished iron-based superconducting strip is prepared by adopting multi-section heat treatment. The strip prepared by the method is high in mechanical strength, uniform and complete in structure, good in chemical stability, high in density and good in texture degree, thereby having high-level superconducting performance. The preparation method disclosed by the invention can be realized under conventional environmental conditions, the process is relatively simple, the selected materials are widely applied to industrial production, and the cost is relatively low, so that the preparation method has very strong feasibility in the aspects of large-scale production and practical application of the strip.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of superconducting materials, and particularly relates to a large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer sheath. Background Art

[0002] Iron-based superconducting materials have attracted much attention due to their excellent physical properties. Among them, 122-type iron-based superconducting materials (such as Ba 1-x K x Fe 2 As 2 、Sr 1-x K x Fe 2 As 2 etc.) have a relatively high critical transition temperature (T c = 38K), an extremely high upper critical field (H c2 > 100T) and a relatively low level of anisotropy value (γ < 2). At the same time, under high magnetic field conditions, the material still has excellent current transmission characteristics. Therefore, 122-type iron-based superconducting materials have strong application prospects.

[0003] Preparing iron-based superconducting materials into wires and tapes is conducive to practical applications. High-quality superconducting wire and tape should have the following characteristics: First, the sheath has good chemical stability, and no chemical reaction occurs between the sheaths and between the sheath and the superconducting core under high-temperature conditions; Second, the wire and tape have a relatively high and appropriate mechanical strength to prevent torsion and bending of the material caused by external factors such as electromagnetic force in a high magnetic field environment; Third, each component of the wire and tape needs to have good cooperative deformation ability to ensure the integrity of the core wire and sheath structure during the processing process.

[0004] To adapt to industrial production and achieve large-scale preparation of iron-based superconducting tapes, it is crucial to simplify the process, reduce costs, and enhance the mechanical strength of the wire tapes. The powder-in-tube method is a simple and efficient way to prepare iron-based superconducting wire tapes. Although traditional silver sheaths have high chemical stability and good workability, their high cost and low mechanical strength limit large-scale applications. Using a composite sheath is a good solution. Sheaths such as iron, stainless steel, and Monel have high mechanical strength, but they are prone to fracture during cold working and are not suitable for large-scale manufacturing. The composite sheath composed of copper and silver has good workability, but during heat treatment, to prevent the liquid phase generated by the alloying of copper and silver, the heat treatment temperature of the copper-silver composite sheath wire tapes is usually lower than the optimal temperature, which will limit the recovery and recrystallization process of superconducting grains, thereby reducing the current-carrying performance of the superconducting wire tapes. To avoid the above situation, a barrier layer (such as niobium, titanium, tantalum, etc.) can be added between copper and silver. The barrier layer is inert to both copper and silver, can prevent the alloying between copper and silver, and at the same time block the diffusion of elements in the superconducting core to the outer sheath. However, during the flat rolling process, due to the large number of components, the tape with a three-layer sheath is prone to sheath separation, which will easily cause the tape to undulate like a wave, thus affecting the stability of the tape performance. Summary of the Invention

[0005] The object of the present invention is to provide a method for large-scale preparation of iron-based superconducting tapes with a barrier layer as the outer sheath, which can enhance the mechanical strength of the tapes, improve their superconducting properties, reduce costs, and is conducive to realizing the large-scale production of the tapes.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for large-scale preparation of iron-based superconducting tapes with a barrier layer as the outer sheath, which comprises the following steps:

[0008] Step 1: Prepare single-core wire

[0009] Load the iron-based superconducting precursor powder added with dopants into the inner sheath, and the inner sheath is a silver tube. After cold working means such as rotary swaging, pass rolling, and drawing, it is processed into a single-core wire.

[0010] Step 2: Prepare a three-layer structure composite sheath multi-core wire by the copper coating method

[0011] Cut the single-core wire obtained in Step 1 into single-core short wires of equal length, bundle n of them into a bunch, load them into the barrier layer sheath, and then load them into the outermost metal sheath. After cold working means such as rotary swaging and drawing, it is processed into a three-layer structure composite sheath multi-core wire.

[0012] The barrier layer sheath is a metal pipe such as a niobium pipe or a titanium pipe with high mechanical strength and good chemical stability, and the outermost metal sheath is a metal pipe with good ductility, such as a copper pipe;

[0013] Step 3: Preparing a superconducting tape with a barrier layer as an outer sheath by the copper removal method

[0014] Place the multi-core wire obtained in Step 2 in nitric acid. After the outermost metal sheath is completely corroded (the superconducting core remains intact, and the complete barrier layer and inner sheath are retained as a composite sheath with a double-layer structure), clean the wire, and then roll the wire into a tape by flat rolling. After the tape reaches the specified thickness, perform multi-stage heat treatment to obtain a high-performance iron-based superconducting tape with a barrier layer as the outer sheath.

[0015] Furthermore, the iron-based superconducting precursor powder described in Step 1 is Ba 0.6 K 0.4 Fe 2 As 2 or Sr 0.6 K 0.4 Fe 2 As 2 , the dopant is Ag, Zn, Sn, etc., and the doping amount is 4.8 - 5.2 wt% of the mass of the iron-based superconducting precursor powder. The specific preparation method is: mix the four elements of Ba (or Sr), K, Fe, and As according to the stoichiometric ratio of Ba 0.6 K 0.4 Fe 2 As 2 (or Sr 0.6 K 0.4 Fe 2 As 2 ), sinter in an argon atmosphere, grind the precursor bulk into superconducting precursor powder with finer particles, and incorporate the dopant.

[0016] Furthermore, the number n of equal-length single-core short wires bundled and loaded into the barrier layer sheath in Step 2 is 6 or 7.

[0017] Furthermore, the drawing process in Step 2 also includes an annealing treatment (i.e., introducing an annealing process before rolling in Step 3).

[0018] Furthermore, during the rolling process in Step 3, when the flat-rolled tape reaches a thickness of 1.00 mm, perform an annealing treatment, and then continue to roll the tape to the specified thickness (i.e., introducing an annealing process during the rolling in Step 3).

[0019] Furthermore, the final specified thickness of the tape described in Step 3 is 0.30 - 0.50 mm.

[0020] Further, the multi-stage heat treatment process described in Step 3 is specifically as follows: The strip is sealed in a vacuum quartz tube and heated from room temperature to 400 °C in an argon atmosphere and held for 1 - 3 h, then heated to 700 °C and held for 1 h, then heated to 850 °C and held for 1 h, then cooled to 600 °C and held for 1 h, and finally cooled in the furnace.

[0021] The present invention adopts the above technical solutions to propose an innovative process for copper-clad drawn wire and copper-removed rolled strip. First, a three-layer composite sheathed iron-based superconducting wire with copper as the outermost layer, a barrier layer material as the second outermost layer, and silver as the inner layer is prepared. Then, the copper sheath is completely corroded, and the barrier layer is used as the outer sheath to roll the strip with a flat roll, and an annealing process is added during the rolling process to release the processing stress and improve the deformation uniformity. Finally, a multi-stage heat treatment is used to obtain the finished iron-based superconducting strip. Nb with excellent plastic deformation is selected to prepare the Nb / Ag composite sheath, and Ti with low cost and high mechanical strength that has been widely used in industry is selected to prepare the Ti / Ag composite sheath. On the one hand, the cost is reduced, and on the other hand, the mechanical strength of the strip is improved. By adjusting the component ratio of the sheath and applying an appropriate intermediate annealing process, high-performance Nb / Ag composite sheath or Ti / Ag composite sheath superconducting strips are prepared by a low-cost method of conventional sintering.

[0022] The technical solution of the present invention has the following advantages:

[0023] 1. The Cu / Nb / Ag and Cu / Ti / Ag composite sheaths used for the iron-based superconducting wire have reduced costs, high mechanical strength, and good chemical stability, laying a foundation for the preparation of high-performance iron-based superconducting strips. The present invention uses a composite sheath to replace the traditional pure Ag material as the sheath of the wire and strip, which is beneficial to reducing the cost of the wire and strip and is more conducive to large-scale production and commercial application. By adding a layer of hard barrier layer Nb or Ti between the previous Cu / Ag composite sheaths, not only the mechanical strength of the sheath is improved, ensuring the integrity and uniformity of the wire and strip sheath and the core wire during the cold processing process, but also the chemical stability of the wire and strip is improved, preventing the formation of a liquid phase due to alloying of Cu and Ag elements during the high-temperature heat treatment process, and avoiding the performance decay of the wire and strip due to element diffusion of components such as Cu, Ag, and the iron-based superconducting core.

[0024] 2. A process of combining copper removal rolling and annealing optimization to prepare high-performance iron-based superconducting tapes. Due to the non-uniform mechanical properties among components, in the process of flat rolling the Cu / Nb / Ag or Cu / Ti / Ag three-layer composite sheathed wire into a tape, the outermost Cu sheath with relatively soft texture is prone to separation from the sub-outer Nb or Ti barrier layer material with relatively hard texture. This will reduce the density and texture of the superconducting core in the tape, having a negative effect on the performance of the superconducting tape. Based on this, the present invention proposes a new process of pre-corroding the outermost Cu sheath of the wire with nitric acid before rolling the tape. It should be noted that the barrier layer Nb or Ti materials used in the present invention all have good corrosion resistance. During the reaction of the composite sheath with nitric acid, the Nb or Ti materials can effectively protect the internal Ag sheath and superconducting core from being corroded by nitric acid, and only the Cu material is completely corroded and removed, which makes this process feasible. The flat rolling process is prone to cause relatively rapid work hardening of the tape. Therefore, based on the copper removal rolling of the tape, annealing is carried out twice, respectively before rolling after corrosion and during the rolling process, to optimize various properties of the superconducting tape such as mechanical strength, grain connectivity, and density.

[0025] 3. The iron-based superconducting tape adopts a multi-stage heat treatment method to improve its performance. The first-stage low-temperature heat treatment can improve the bonding degree between the Nb or Ti sheath and the inner Ag sheath in the heating state; the second-stage medium-temperature heat treatment can promote the integrity and formability of the iron-based superconducting core macroscopically. At the same time, volatile elements such as K have participated in the reaction at this time, avoiding their large amount of volatilization and loss due to high temperature; the third-stage high-temperature heat treatment enables the superconducting core to fully react to generate a superconducting phase, effectively improving the connectivity of grains, thereby improving the superconducting performance; the fourth-stage sub-low-temperature heat treatment during the cooling process aims to make the superconducting phase generated under high-temperature conditions more stable, and stable performance is the premise for large-scale preparation and wide application.

[0026] 4. Adopt a low-cost conventional preparation method. The raw materials such as metal pipes and precursor powders used in the present invention, cold working equipment such as rotary forging machines, rolling mills, and broaching machines, and heat treatment equipment such as tube furnaces are all very popular in the scenario of preparing wire tapes. The powder-in-tube method adopted is also an extremely convenient preparation method. The tapes prepared by conventional heat treatment means without pressure can also have comparable performance to the tapes prepared under partial pressure conditions, which can reduce the cost in industrial production and realize large-scale application. Description of the Drawings

[0027] The following further describes the present invention in detail in conjunction with the drawings and specific embodiments;

[0028] Figure 1 For the composite sheath Ba 0.6 K 0.4 Fe 2 As 2Schematic structural diagram of a 7-core wire, where the composite sheath in the left figure is a Cu / Nb / Ag or Cu / Ti / Ag sheath before corrosion, and the composite sheath in the right figure is a Nb / Ag or Ti / Ag sheath after corrosion.

[0029] Figure 2 Ti / Ag composite sheath Ba with a thickness of 0.45 mm 0.6 K 0.4 Fe 2 As 2 Optical micrograph of the cross-section of a 7-core strip.

[0030] Figure 3 Nb / Ag and Ti / Ag composite sheath Ba 0.6 K 0.4 Fe 2 As 2 Physical appearance diagram of the strip.

[0031] Figure 4 For the preparation of composite sheath Ba 0.6 K 0.4 Fe 2 As 2 Process flow chart of the wire strip.

[0032] Figure 5 Multi-stage heat treatment curve graph. Specific implementation manner

[0033] In order to make the purpose, technical route and advantages of the present invention clearer, the following further illustrates the present invention in combination with embodiments and drawings. The embodiments are only used to explain the present invention and are not used to limit the present invention.

[0034] Example 1

[0035] A large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer sheath

[0036] (1) Preparation of superconducting precursor powder

[0037] Mix and grind the four elements of Ba, K, Fe, and As according to the chemical stoichiometric ratio of 0.6:0.4:2:2, fill them into an Nb tube, place it in a stainless steel tube and weld it firmly, and sinter it at 900 °C for 40 h in an argon atmosphere. After sintering, take out the precursor bulk material and grind it into precursor powder, dope 5 wt% of dopant Ag into the precursor powder, and grind and mix evenly to prepare the doped Ba 0.6 K 0.4 Fe 2 As 2 Superconducting precursor powder.

[0038] (2) Preparation of Ag-sheathed single-core wire

[0039] Weigh 12 g of the doped Ba 0.6 K 0.4 Fe 2 As 2 superconducting precursor powder. Using the ex-situ powder-in-tube method (ex-situ PIT), fill the powder into an Ag tube with an outer diameter of 7.00 mm and an inner diameter of 4.70 mm, and tightly seal both ends of the tube with aluminum plugs. Rotary forge the Ag tube containing the powder for 2 passes until the outer diameter is about 6.30 mm. Use a grooved rolling mill to roll the wire for 4 passes until the outer diameter is 4.80 mm, and then draw the wire to an outer diameter of 2.54 mm to obtain an Ag-sheathed single-core wire.

[0040] (3) Preparation of Cu / Nb / Ag composite-sheathed 7-core wire

[0041] Cut 7 equal-length Ag-sheathed single-core wires with an outer diameter of 2.54 mm, bundle them and load them into an Nb tube with an outer diameter of 10.00 mm and an inner diameter of 8.00 mm, and then put the Nb tube into a Cu tube with an outer diameter of 12.00 mm and an inner diameter of 10.00 mm. The structure is as Figure 1 shown. Start drawing after rotary forging to an outer diameter of about 9.50 mm. Since processing stress will be generated during the drawing process, when the wire is drawn to an outer diameter of 4.30 mm, intermediate annealing is carried out. The annealing regime is annealing at 500 °C for 90 min, and then the wire is drawn to an outer diameter of 2.18 mm.

[0042] (4) Preparation of superconducting tape by combining copper removal rolling and annealing optimization

[0043] Flatten both ends of the Cu / Nb / Ag composite-sheathed 7-core wire with an outer diameter of 2.18 mm and place it in nitric acid. After the reaction ends, the Cu sheath is completely corroded, and the Nb / Ag composite sheath and the superconducting core remain intact. At this time, the wire diameter is about 1.80 mm. Clean the surface of the wire with a large amount of clean water and alcohol, ultrasonically clean and dry it. Place the Nb / Ag-sheathed wire in a tube furnace and anneal it at 700 °C for 1 h under vacuum conditions. Roll the wire with flat rolls to a thickness of 1.00 mm, introduce a primary intermediate annealing process, and the annealing regime is still annealing at 700 °C for 1 h to release the stress of the tape during cold rolling. After intermediate annealing, continue rolling to a thickness of 0.45 mm. The above process is rolled for 6 passes, and the thickness deformation rate of each pass is controlled at 15%-25%.

[0044] (5) Preparation of high-performance tape products by multi-stage heat treatment method

[0045] Seal the tape in a vacuum quartz tube, and in an argon atmosphere, heat and cool at a rate of 5 °C / min. First heat from room temperature to 400 °C and hold for 3 h, then heat to 700 °C and hold for 1 h, then heat to 850 °C and hold for 1 h, then cool to 600 °C and hold for 1 h, and finally cool with the furnace. The specific heat treatment temperature curve is asFigure 5 As shown. Through test and analysis, it is found that the strip groove is uniform, the structure is complete, without rupture phenomenon, the superconducting core wires have good longitudinal uniformity, and the sausage effect does not occur; the superconducting core phase has high purity and good texture, about 0.50; no element diffusion phenomenon occurs in the cladding and the superconducting core, and no reaction layer is formed; the Vickers hardness of the superconducting core reaches 160 Hv, and the density is high; the critical transition temperature T c reaches 37.3 K.

[0046] Example 2

[0047] A large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer cladding

[0048] (1) Preparation of superconducting precursor powder

[0049] Mix and grind the four elements of Ba, K, Fe, and As according to the chemical stoichiometric ratio of 0.6:0.4:2:2, fill them into an Nb tube, put it into a stainless steel tube and weld it firmly, and sinter it at 900 °C for 40 h in an argon atmosphere. After sintering, take out the precursor bulk material and grind it into precursor powder, dope 5 wt% of the dopant Sn into the precursor powder, and grind and mix it evenly to prepare the doped Ba 0.6 K 0.4 Fe 2 As 2 superconducting precursor powder.

[0050] (2) Preparation of Ag-clad single-core wire

[0051] Weigh 15 g of the doped Ba 0.6 K 0.4 Fe 2 As 2 superconducting precursor powder. Adopt the ex-situ powder-in-tube method (ex-situ PIT), fill the powder into an Ag tube with an outer diameter of 8.30 mm and an inner diameter of 6.10 mm, and press and seal both ends of the tube with aluminum plugs. Rotary forge the Ag tube filled with powder to an outer diameter of about 7.20 mm, use a grooved rolling mill to roll the wire for 3 passes to an outer diameter of 5.50 mm, and then draw the wire to an outer diameter of 2.54 mm to obtain an Ag-clad single-core wire.

[0052] (3) Preparation of Cu / Nb / Ag composite-clad 7-core wire

[0053] Cut 7 equal-length Ag-clad single-core wires with an outer diameter of 2.54 mm, bundle and load them into an Nb tube with an outer diameter of 10.00 mm and an inner diameter of 8.00 mm, and then put the Nb tube into a Cu tube with an outer diameter of 12.00 mm and an inner diameter of 10.00 mm. The structure is as Figure 1As shown in the figure. Rotary forging is carried out until the outer diameter reaches about 9.50 mm, and then wire drawing begins. Since processing stress will be generated during wire drawing, when the wire is drawn to an outer diameter of 4.30 mm, intermediate annealing is carried out, and the annealing regime is annealing at 500 °C for 90 min. After that, the wire is drawn to an outer diameter of 2.18 mm.

[0054] (4) Preparation of superconducting tapes by combining copper removal rolling and annealing optimization

[0055] The two ends of the Cu / Nb / Ag composite sheathed 7-core wire with an outer diameter of 2.18 mm are flattened and placed in nitric acid. After the reaction ends, the Cu sheath is completely corroded, and the Nb / Ag composite sheath and the superconducting core remain intact. At this time, the wire diameter is about 1.80 mm. The surface of the wire is cleaned with a large amount of water and alcohol, ultrasonically cleaned and dried. The Nb / Ag sheathed wire is placed in a tube furnace and annealed at 700 °C for 1 h under vacuum conditions. The wire is flat-rolled to a thickness of 1.00 mm, and an intermediate annealing process is introduced. The annealing regime is still annealing at 700 °C for 1 h to release the stress of the tape during cold rolling. After intermediate annealing, it is continuously rolled to a thickness of 0.45 mm. The above process is rolled for 6 passes, and the thickness deformation rate of each pass is controlled at 15%-25%.

[0056] (5) Preparation of high-performance tape products by multi-stage heat treatment method

[0057] The tape is sealed in a vacuum quartz tube. In an argon atmosphere, the temperature is raised and lowered at a rate of 5 °C / min. First, it is heated from room temperature to 400 °C and held for 3 h, then heated to 700 °C and held for 1 h, then heated to 850 °C and held for 1 h, and then cooled to 600 °C and held for 1 h. Finally, it is cooled with the furnace. The specific heat treatment temperature curve is as Figure 5 shown. Through test analysis, it is found that the tape has a uniform hole shape, a complete structure, no cracking phenomenon, good longitudinal uniformity of the superconducting core filaments, and no sausage effect; the superconducting core has a high phase purity and a good texture degree, about 0.50; no element diffusion phenomenon occurs in the sheath and the superconducting core, and no reaction layer is formed; the Vickers hardness of the superconducting core reaches 158 Hv, and the density is high; the critical transition temperature T c reaches 37.3 K.

[0058] Example 3

[0059] A large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer sheath

[0060] (1) Preparation of superconducting precursor powder

[0061] Mix 0.6:0.4:2:2 of Ba, K, Fe, and As elements by chemical stoichiometric ratio, grind them, fill them into a Ti tube, place it in a stainless-steel tube and weld it firmly, and sinter it at 900 °C for 40 h in an argon atmosphere. After sintering, take out the precursor bulk material, grind it into precursor powder, dope 5 wt% of the dopant Ag into the precursor powder, and grind and mix them evenly to prepare the doped Ba 0.6 K 0.4 Fe 2 As 2 superconducting precursor powder.

[0062] (2) Preparation of Ag-sheathed single-core wire

[0063] Weigh 12 g of the doped Ba 0.6 K 0.4 Fe 2 As 2 superconducting precursor powder. Adopt the ex-situ powder-in-tube method (ex-situ PIT), fill the powder into an Ag tube with an outer diameter of 7.00 mm and an inner diameter of 4.70 mm, and press and seal both ends of the tube with aluminum plugs. Rotate and forge the Ag tube containing the powder for 2 passes to an outer diameter of about 6.30 mm, use a grooved rolling mill to roll the wire for 4 passes to an outer diameter of 4.80 mm, and then draw the wire to an outer diameter of 1.89 mm to obtain an Ag-sheathed single-core wire.

[0064] (3) Preparation of Cu / Ti / Ag composite-sheathed 7-core wire

[0065] Cut 7 equal-length Ag-sheathed single-core wires with an outer diameter of 1.89 mm, bundle them and load them into a Ti tube with an outer diameter of 8.00 mm and an inner diameter of 6.00 mm, and then put the Ti tube into a Cu tube with an outer diameter of 10.00 mm and an inner diameter of 8.00 mm. The structure is as Figure 1 shown. Start drawing after rotary forging to an outer diameter of about 9.50 mm. Since processing stress will be generated during the drawing process, when the wire is drawn to an outer diameter of 4.30 mm, intermediate annealing is carried out. The annealing regime is annealing at 500 °C for 90 min, and then the wire is drawn to an outer diameter of 2.18 mm.

[0066] (4) Preparation of superconducting tape by combining copper-removing rolling and annealing optimization

[0067] The two ends of a Cu / Ti / Ag composite sheathed 7-core wire with an outer diameter of 2.18 mm were flattened and placed in nitric acid. After the reaction ended, the Cu sheath was completely corroded, while the Ti / Ag composite sheath and the superconducting core remained intact. At this time, the wire diameter was approximately 1.70 mm. A large amount of water and alcohol were used to clean the surface of the wire, which was then ultrasonically cleaned and dried. The Ti / Ag sheathed wire was placed in a tube furnace and annealed at 700 °C for 1 h under vacuum conditions. The wire was flat-rolled to a thickness of 1.00 mm, and an intermediate annealing process was introduced. The annealing regime was still 700 °C for 1 h to relieve the stress of the strip during cold rolling. After the intermediate annealing, it was continuously rolled to a thickness of 0.45 mm. The above process is the fast rolling method, with a total of 6 rolling passes, and the thickness deformation rate of each pass is controlled at 15%-25%. Figure 2 It is an optical micrograph of the cross-section of the strip.

[0068] (5) Preparation of high-performance strip products by a multi-stage heat treatment method

[0069] The strip was sealed in a vacuum quartz tube and heated and cooled at a rate of 5 °C / min in an argon atmosphere. It was first heated from room temperature to 400 °C and held for 3 h, then heated to 700 °C and held for 1 h, then heated to 850 °C and held for 1 h, and then cooled to 600 °C and held for 1 h, and finally cooled with the furnace. The specific heat treatment temperature curve is as Figure 5 shown. Through test analysis, it was found that the strip had a uniform pore shape, a complete structure, no cracking phenomenon, good longitudinal uniformity of the superconducting core filaments, and no sausage effect; the superconducting core had a high phase purity and a good texture, about 0.53; there was no element diffusion phenomenon in the sheath and the superconducting core, and no reaction layer was formed; the Vickers hardness of the superconducting core reached 180 Hv and the density was high; the critical transition temperature T c reached 37.5 K.

[0070] Example 4

[0071] A large-scale preparation method of an iron-based superconducting strip with a barrier layer as an outer sheath

[0072] (1) Preparation of superconducting precursor powder

[0073] The four elements Ba, K, Fe, and As were mixed and ground according to the chemical stoichiometric ratio of 0.6:0.4:2:2, filled into a Ti tube, placed in a stainless steel tube and welded firmly, and sintered at 900 °C for 40 h in an argon atmosphere. After sintering, the precursor bulk was taken out, ground into precursor powder, doped with 5 wt% of the dopant Ag based on the mass of the precursor powder, and ground and mixed evenly to prepare the doped Ba 0.6 K 0.4 Fe 2 As 2 superconducting precursor powder.

[0074] (2) Preparation of Ag-clad single-core wire

[0075] Weigh 12 g of the doped Ba 0.6 K 0.4 Fe 2 As 2 superconducting precursor powder. Using the ex-situ powder-in-tube method (ex-situ PIT), fill the powder into an Ag tube with an outer diameter of 7.00 mm and an inner diameter of 4.70 mm, and tightly seal both ends of the tube with aluminum plugs. Rotate and forge the Ag tube containing the powder for 2 passes to an outer diameter of about 6.30 mm, use a grooved rolling mill to roll the wire for 4 passes to an outer diameter of 4.80 mm, and then draw the wire to an outer diameter of 1.89 mm to obtain the Ag-clad single-core wire.

[0076] (3) Preparation of Cu / Ti / Ag composite-clad 7-core wire

[0077] Cut 7 equal-length Ag-clad single-core wires with an outer diameter of 1.89 mm, bundle them and load them into a Ti tube with an outer diameter of 8.00 mm and an inner diameter of 6.00 mm, and then put the Ti tube into a Cu tube with an outer diameter of 10.00 mm and an inner diameter of 8.00 mm. The structure is as Figure 1 shown. Start drawing after rotary forging to an outer diameter of about 9.50 mm. Since processing stress will be generated during the drawing process, when the wire is drawn to an outer diameter of 4.30 mm, intermediate annealing is carried out. The annealing regime is annealing at 500 °C for 90 min, and then the wire is drawn to an outer diameter of 2.18 mm.

[0078] (4) Preparation of superconducting tape by combining copper removal rolling and annealing optimization

[0079] Flatten both ends of the Cu / Ti / Ag composite-clad 7-core wire with an outer diameter of 2.18 mm and place it in nitric acid. After the reaction ends, the Cu cladding is completely corroded, and the Ti / Ag composite cladding and the superconducting core remain intact. At this time, the wire diameter is about 1.70 mm. Clean the surface of the wire with a large amount of water and alcohol, ultrasonically clean and dry it. Place the Ti / Ag-clad wire in a tube furnace and anneal it at 700 °C for 1 h under vacuum conditions. Roll the wire with flat rolls to a thickness of 1.00 mm, introduce a primary intermediate annealing process, and the annealing regime is still annealing at 700 °C for 1 h to release the stress of the tape during cold rolling. After intermediate annealing, continue rolling to a thickness of 0.45 mm. The above process is the slow rolling method, with a total of 8 passes, and the thickness deformation rate of each pass is controlled at 10%-23%.

[0080] (5) Preparation of high-performance tape products by multi-stage heat treatment method

[0081] The strip is sealed in a vacuum quartz tube, and the temperature is raised and lowered at a rate of 5 °C / min in an argon atmosphere. First, it is heated from room temperature to 400 °C and held for 3 h, then heated to 700 °C and held for 1 h, then heated to 850 °C and held for 1 h, then cooled to 600 °C and held for 1 h, and finally cooled in the furnace. The specific heat treatment temperature curve is as shown in Figure 5 . Through test analysis, it is found that the strip has a uniform hole pattern, a complete structure, no cracking phenomenon, good longitudinal uniformity of the superconducting core wires, and no sausage effect; the superconducting core phase has a high purity and a good texture, about 0.53; no element diffusion phenomenon occurs in the cladding and the superconducting core, and no reaction layer is formed; the Vickers hardness of the superconducting core reaches 180 Hv, and the density is high; the critical transition temperature T c reaches 37.5 K.

Claims

1. A large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer sheath, characterized in that: It includes the following steps: Step 1: Prepare the single-core wire The iron-based superconducting precursor powder to which dopants have been added is placed into an inner sheath, and processed into a single-core wire by rotary forging, groove rolling, and drawing; the inner sheath is a silver tube; Step 2: Preparation of three-layer composite sheathed multi-core wire by copper cladding method The single-core wire obtained in step 1 is cut into single-core short wires of equal length, and n wires are bundled into a barrier layer sheath, and then the outermost metal sheath is put into the bundle, and then the three-layer structure composite sheath multi-core wire is processed by rotary forging and drawing; The barrier layer sheath is a niobium tube or a titanium tube, and the outermost metal sheath is a copper tube; Step 3: Preparation of superconducting tape with barrier layer as outer sheath by copper removal method The multi-core wire obtained in step 2 is placed in nitric acid. After the outermost metal sheath is completely corroded, the wire is cleaned and then rolled into a strip by a flat roller. After the strip reaches a specified thickness, it is subjected to multi-stage heat treatment to obtain an iron-based superconducting strip with a barrier layer as an outer sheath.

2. The method for large-scale preparation of an iron-based superconducting tape with a barrier layer as an outer sheath according to claim 1, characterized in that: The iron-based superconducting precursor powder described in step 1 is Ba 0.6 K 0.4 Fe2As2 or Sr 0.6 K 0.4 Fe2As2, dopant is Ag, Zn or Sn, doping amount is 4.8~5.2% of the mass of iron-based superconducting precursor powder wt %.

3. The large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer sheath according to claim 1, characterized in that: In step 2, the number n of single-core short wires of equal length bundled and packed into the barrier layer sheath is 6 or 7.

4. The large-scale preparation method of an iron-based superconducting tape with a barrier layer as an outer sheath according to claim 1, characterized in that: The drawing process in step 2 also includes annealing treatment.

5. The method for large-scale preparation of an iron-based superconducting tape with a barrier layer as an outer sheath according to claim 1, characterized in that: Step 3: During the rolling process, when the flat roll rolls the strip to a thickness of 1.00 mm, annealing is performed, and after annealing, the strip is further rolled to a specified thickness.

6. The method for large-scale preparation of an iron-based superconducting tape with a barrier layer as an outer sheath according to claim 1, characterized in that: The strip described in step 3 has a final specified thickness of 0.30-0.50 mm.

7. The method for large-scale preparation of an iron-based superconducting tape with a barrier layer as an outer sheath according to claim 1, characterized in that: The multi-stage heat treatment process described in step 3 is specifically as follows: the strip is sealed in a vacuum quartz tube, heated from room temperature to 400°C in an argon atmosphere for 1 to 3 hours, then heated to 700°C for 1 hour, then heated to 850°C for 1 hour, then cooled to 600°C for 1 hour, and finally cooled in the furnace.

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